Mostly because he wasted time healing Freeza with his Ki donation and blasting him and stuff. It's difficult to say how it'd have gone if that didn't happen and he decided to go for the kill. I can see the argument that he'd run out of time though, since Freeza's stamina would last longer in this case.To be fair, I can see Freeza maybe lasting long enough so Goku would die on Namek's explosion. Didn't Goku escape on the very last second?
I'd say a bit is an understatement. He couldn't even open one of his eyes. That and his tail make it look like it wasn't an ordinary injury. Not to mention he said "I'm still more than a match for you," implying that he did lose some Ki or stamina at the very least.I don't think anything actually affected Freeza's Ki since he was just roughed up a bit, but Goku was definitely on his last legs. He got a crazy amount of Deus Ex Machina with his infinite stamina and telepathy.
I'd still say his power once he actually buffed up and reached 100% was his true full power. SSJ3 Goku after taking some damage and stamina loss from fighting Kid Boo for a couple of minutes thought he could reach his maximum power by charging his Ki. And if it was like those other cases where injuries/stamina loss hindered their full potential Freeza or Goku would say it, esp since Goku was obsessed with besting Freeza at his best.I'd say a bit is an understatement. He couldn't even open one of his eyes. That and his tail make it look like it wasn't an ordinary injury. Not to mention he said "I'm still more than a match for you," implying that he did lose some Ki or stamina at the very least.